When underground uranium undergoes radioactive decay one product eventually formed is the radioactive gas radon. The radon migrates to the surface where the alpha and beta rays it emits can be uniquely detected by dosimeters.
Commonly used dosimeters contain a material such as cellulose nitrate which the alpha particles damage when they traverse it, leaving tracks. The tracks are etched in a reagent such as sodium hydroxide to enlarge them. They are then counted under a microscope to give an indication of the size and location of the uranium deposits. (See U.S. Pat. No. 3,665,194.) these dosimeters are expensive to read and can only be used once. Also the tracks tend to anneal out at about 120.degree. F., limiting their use in hot climates.